1. Field of the Invention
The present invention relates to a repetitive call control method, a switch using the method, and a recording medium storing repetitive call control program. More particularly, the present invention is concerned with detection and control of a repetitive call that occurs in a network including a switch.
2. Description of the Related Art
Recently, a switch network is constructed by mutual connections of common carriers. Each switch station included in the switch network performs setting of an outgoing path for determining a route through which a call passes. All switch stations in the switch network should be synchronized with each other with regard to the setting of outgoing paths.
In order to change the route through which the call passes, all the switch stations of different carriers are required to concurrently change the setting of outgoing paths. If the concurrent change does not take place, an asynchronous situation will occur in which the setting of outgoing paths does not match among the switch stations. When a bypass route is used to transmit the call, a complex procedure for setting of call outgoing paths must be performed in the switch stations of the carriers. Thus, there is a possibility that an error in setting of outgoing paths may occur. An error in setting of an outgoing path may cases a repetitive call in which a call occupies channels in an identical channel group in the switch network.
FIG. 1 is a diagram illustrating a mechanism of occurrence of a repetitive call. There is an error in setting of an outgoing path (channel) in a station (B) 14. The station 14 erroneously sets a channel xe2x80x9cbexe2x80x9d with respect to a call directed to a station (C) 16 and initiated by a station (A) 12. When a calling subscriber 10 calls a destination subscriber 22, the station 14 erroneously sets the channel xe2x80x9cbexe2x80x9d although originally the station 14 should set an outgoing channel xe2x80x9cbcxe2x80x9d. A station (E) 20 determines that the call should be addressed to the station 16, and sets an outgoing channel xe2x80x9cebxe2x80x9d.
Thus, a group of channels xe2x80x9cbexe2x80x9d and xe2x80x9cebxe2x80x9d are constantly used by a repetitive call, so that a congestion of channels xe2x80x9cbexe2x80x9d and xe2x80x9cebxe2x80x9d occurs. If a station (D) 18 is available as a bypass route in a case where the channel xe2x80x9cebxe2x80x9d is congested, channels xe2x80x9cedxe2x80x9d and xe2x80x9cdbxe2x80x9d will be congested by a repetitive call.
If an error in the setting of a bypass route, a repetitive call may occur in the switch network. FIG. 2 shows another example of occurrence of a repetitive call. Referring to FIG. 2, it is assumed that a first outgoing channel for a call from the station 14 to the station 16 is xe2x80x9cbcxe2x80x9d, a second outgoing channel is xe2x80x9cbexe2x80x9d and that a first outgoing channel for a call from the station 20 to the station 16 is xe2x80x9cecxe2x80x9d and a second outgoing channel is xe2x80x9cebxe2x80x9d.
If the channels xe2x80x9cbcxe2x80x9d and xe2x80x9cecxe2x80x9d are congested, the stations 14 and 20 will set the second outgoing channels as those for forming bypass routes. If the station 14 initiates a call directed to the station 16, a group of channels xe2x80x9cbexe2x80x9d and xe2x80x9cebxe2x80x9d is constantly used by a repetitive call until the channels xe2x80x9cbcxe2x80x9d and xe2x80x9cecxe2x80x9d are recovered from the congested states. Thus, the channels xe2x80x9cbexe2x80x9d and xe2x80x9cebxe2x80x9d will be congested.
FIGS. 3A and 3B show a conventional method for resolving the problem of the repetitive call. A switch network shown in FIG. 3A includes a table shown in FIG. 3B. For example, the station 14 is equipped with the table shown in FIG. 3B. The table describes information indicating whether an outgoing channel is allowed to be connected to an incoming channel via which a call is transferred.
In a case where channel xe2x80x9cebxe2x80x9d is an incoming channel of the station 14 and xe2x80x9cbexe2x80x9d is an outgoing channel thereof, the station 14 prevents the call from the channel xe2x80x9cebxe2x80x9d to be output to the channel xe2x80x9cbexe2x80x9d again.
FIGS. 4A and 4B show another conventional method for resolving the problem of the repetitive call. The station 14 in a network shown in FIG. 4A is equipped with a table shown in FIG. 4B. The table shown in FIG. 4B describes information the ratio of occupation in an outgoing channel for each call type.
If the type of a call over incoming channel xe2x80x9cabxe2x80x9d to the station 14 differs from that of a call over incoming channel xe2x80x9cebxe2x80x9d, outgoing channel xe2x80x9cbexe2x80x9d is not occupied by one of the two incoming channels xe2x80x9cabxe2x80x9d and xe2x80x9cebxe2x80x9d even if a repetitive call occurs. Thus, even in a case where a loop is formed between the stations 14 and 20, a group of the channels xe2x80x9cbexe2x80x9d and xe2x80x9ceb2xe2x80x9d is not occupied by the repetitive call, so that the channels xe2x80x9cbexe2x80x9d and xe2x80x9cebxe2x80x9d can be prevented from being congested.
However, the methods for controlling the repetitive call shown in FIGS. 3A, 3B and FIGS. 4A and 4B are not capable of detecting occurrence of a repetitive call in real time. That is, the maintenance person predicts occurrence of a repetitive call and takes measures against occurrence of a repetitive call and spreading of an unwanted situation. In practice, it is very difficult to seize a situation of occurrence of a repetitive call and look into a cause thereof.
More particularly, the repetitive call controlling method shown in FIGS. 3A and 3B does not cope with a repetitive call coming from a channel which is not registered in the table shown in FIG. 3B. If information indicating whether a connection should be made is registered with respect to all incoming and outgoing channels, the switch stations will be needed to have increased inner resources such as a CPU and a memory. In addition, it is required to process a huge amount of data for setting outgoing channels so that maintenance cannot be performed reliably.
The repetitive call controlling method as shown in FIGS. 4A and 4B determines the ratio of occupation for each call type in advance. Thus, the method does not have wide applicability to various networks and does not utilize the channels efficiently.
As yet another means for controlling repetitive calls, it may be possible to integrally manage information concerning setting of outgoing channels and the current situation in real time. An intelligent network is equipped with means as described above. However, the means does not acknowledge, as a problem, a repetitive call resulting from a situation in which the setting of a bypass route is erroneously set, as shown in FIG. 2 because information itself concerning setting of an outgoing channel does not have any problem.
It is a general object of the present invention to provide a repetitive call control method and a switch using the method.
A more specific object of the present invention is to provide a repetitive all control method and a switch using the method capable of automatically detecting and imposing a restriction on a repetitive call and preventing occurrence of a congested situation.
The above objects of the present invention are achieved by a switch comprises: a repetitive call detection unit which detects a repetitive call which occupies channels in an identical channel group; a release unit which releases the channels occupied by the repetitive call when the repetitive call is detected; a restriction unit which stores information concerning the repetitive call and imposes a restriction on a connection of a call having information identical to the information concerning the repetitive call; a test unit which determines whether a cause of the repetitive call has been removed; and a restriction release unit which releases the above restriction in accordance with a result of determination by the test unit.
The above objects of the present invention are also achieved by a method comprising the steps of: detecting a repetitive call which occupies channels in an identical channel group; releasing the channels occupied by the repetitive call when the repetitive call is detected; storing information concerning the repetitive call and imposing a restriction on a connection of a call having information identical to the information concerning the repetitive call; determining whether a cause of the repetitive call has been removed; and releasing the above restriction in accordance with a result of determination by the test unit.
According to the above-mentioned switch and method, it is possible to drastically reduce the number of channels occupied by a repetitive call and to prevent the system from being congested. Further, it is possible to impose a restriction on a connection of a call similar to a repetitive call.
The switch may be configured so that it further comprises a notify unit which notifies given positions of associated stations of information concerning the repetitive call detected. Thus, it is possible to automatically notify maintenance persons or the like involved in their own station or an adjacent station of information concerning the repetitive call. Thus, these stations can share information concerning the repetitive call, so that a cause of the repetitive call can efficiently be removed.
The above switch may be configured so that the repetitive call detection unit comprises: a first unit which reads call information concerning calls that use the channels from a given table; and a second unit which compares the call information read with call information concerning a current call and determines whether the given table defines a call having call information identical to that of the current call, and wherein, if it is determined that the given table defines a call having call information identical to that of the current call, the current call is acknowledged as a repetitive call. Thus, it is possible to efficiently detect the repetitive call.
The switch may be configured to so that the repetitive call detection unit comprises: a first unit which reads call information concerning calls that use the channels from a given table; and a second unit which compares the call information read with call information concerning a current call and determines whether the given table defines a call having call information identical to that of the current call, and wherein, if it is determined that the given table defines a call having call information identical to that of the current call, the current call is acknowledged as a repetitive call in a case where a time interval between a time when said call having identical call information defined in the table occurs and a time when said current call occurs is equal to or shorter than a given time interval. Thus, it is possible to accurately detect the repetitive call.
The switch may be configured so that if it is determined that the current call is a repetitive call, the repetitive call detection unit registers the call information concerning the current call in the given table. Thus, it is possible to impose a restriction on a call having call information identical to that of the repetitive call registered in the given table.
The switch may be configured so that the test unit comprises: a test call generating unit generating a test call having call information identical to that of the repetitive call at given intervals; a test call sending unit sending the test call to a network to which the switch is connected; and a determination unit which determines that a cause of the repetitive call has not yet been removed if the test call is received before a predetermined time elapses and which determines that the cause of the repetitive call has been removed if the test call is not received before the predetermined time elapses. Thus, it is possible to easily and accurately determine whether a cause of the repetitive call has been eliminated.
The switch may be configured so that the determination unit comprises: a first unit which registers information concerning a situation in which the cause of the repetitive call has not yet been removed if the test call is received before the predetermined time elapses; and a second unit which deletes the call information concerning the repetitive call from the given table if the test call is not received before the predetermined time elapses. It is thus possible to efficiently manage the repetitive call.